Were there any manuals made for the D6600 3 cyl diesel?

When you say "manuals" .. I'm presuming you mean Service Reference Books? .. for overhaul instruction?

The D6600 has no Service Reference Book as such. There is an Operators Instruction Book for D6600 Power Unit, S/N 5E 9668-up .. and that book is form #3480.
There is an Operators Instruction Book for D6600 Power Unit, S/N 5E 9501-9667 .. this is form #3012 .. and is the same book as for the D6100 Power Unit, S/N 4C 9001 - 4C 9180 .. because Cat deemed the engines so similar, that the one book would suffice for both engines.

There does not appear to be a Service Reference book printed specifically for the individual engines of the mid-to-late 1930's.

The only Servicemans Reference book for Diesel engines that I know of .. is the generalized, "Servicemans Reference Book for Caterpillar Diesel Engines" .. form #5060A .. which was released in the late 1930's, and which gives general overhaul guidelines, and basic specifications, for all the Cat Diesels of that era.

This book was reprinted regularly into the early 1940's (possibly well into WW2), before it was deemed necessary to have SRB's for individual engines.

Beaver-Flat - just curious; do you have a D6600 engine you need to work on? GWH

I have an old D6-2H with the D6600 engine. The engine is stuck, so I'll be bringing it into the shop to start working on it.

Hi beaver-flat,
You can check the manuals list for yourself at:
www.cat.com/cda/layout?m=90800&x=7

The tractors are under "track tractors" on page two.

Beaver Flat,
I have a parts catalog that covers up to s/n 2h3247.
Form 8467

I've got a 1941 copy of the form 5060B Serviceman's reference book for Caterpillar diesel engines if you need something like a crankshaft dimension or governor settings. Not really a whole lot else in it as far as specs.

thanks, I'll post needs as I get in the middle of this project. I looked at the CAT site for manuals. Does the OM for the D6600 cover engine repairs and specs? How about the pony?

OM usually doesn't have much as far as specs beyond weights and capacities.

I guess you were supposed to use a fastener torque table, some small amount of data and your experience/training that applied to a broad range of engines with similar components.